The Dragons claimed just their second win of the NRL season on Saturday at Kogarah Oval, with Valentine Holmes scoring a late double to keep the Red V's hopes of avoiding the wooden spoon alive.
But the wash-up will centre on the injury to Koroisau and how that impacts the Tigers' (7-9) chances of making the top eight.
When they have been without their crafty hooker this year, the Tigers have struggled badly and if scans confirm Koroisau needs to undergo surgery his campaign will be over.
Koroisau was loathe to discuss his injury in the post-match press conference, but coach Benji Marshall was happy to left fly at his side, who slipped to 12th.
Marshall's side started the year with a 5-2 record, but have lost seven of their nine games since Jarome Luai announced his intention to quit the club at the end of next season to join the PNG Chiefs.
"We got exactly what we deserved today; discipline, attention to detail, care, wasn't good enough," Marshall said.
"Full credit to the Dragons because they earned their win and we were poor.
"We had a chance to turn up and have a real crack at it, but we weren't good enough, people will want to say it looks like the end of our season but we won't give up."
Luai was not playing as a result of delayed concussion symptoms and it appeared the Tigers would get by without him, when Adam Doueihi took advantage of Clint Gutherson's early sin-binning to put his side ahead after eight minutes.
Doueihi missed the conversion and when Gutherson returned the Dragons looked threatening on the left.
Tyrell Sloan had a try chalked off for a foot in touch before sliding in without a hitch at the second time of asking in the 20th minute.
Sloan succumbed to a hamstring injury on the half-hour mark with Damien Cook forced into the centres and Holmes, who kicked a penalty to give the Dragons a 6-4 halftime lead, moved to the left wing.
Doueihi put the Tigers back in front with his second of the night, the halfback grubbering ahead and pouncing on the ball in the in-goal.
But when the Dragons halted a run of dreadful errors - and Koroisau went off - interim coach Dean Young's side finally found a killer punch.
Holmes crossed twice in the space of five minutes, converting both tries as well as that of Mat Feagai to seal victory late on.
"It's a real credit to them and the way they've been turning up each day," Young said.
"I know they get paid well to it, but the situation the club is in is not easy, but they buy in and we feel like we are getting better.
"The resilience of the team really pleased me."
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